barley

Elite barley breeding lines from the Australian Northern Region Barley Breeding Program were evaluated at the seedling and adult growth stages for resistance to leaf rust (LR) caused by Puccinia hordei. F3:5 lines derived from parental germplasm of different geographic origins were screened in the glasshouse and field spanning four years of trials. The 2009 and 2011 breeding populations (BP1 and BP2) comprised 360 lines and were genotyped with 3,244 polymorphic diversity arrays technology (DArT) markers. The 2012 and 2013 breeding populations (BP3 and BP4) comprised 320 lines genotyped with the DArT GBS array (DArTseq), providing 15,400 high quality polymorphic markers. Association mapping (AM) using the DArT/DArT-seq datasets and phenotypic data from 15 independent LR response assays identified a number of genomic regions associated with resistance. The BP1 and BP2 study detected a total of 15 QTL; 5 QTL co-located with catalogued LR resistance genes (Rph1, Rph3/19, Rph8/14/15, Rph20, and Rph21), 6 QTL aligned with previously reported genomic regions and 4 QTL (3 on chromosome 1H and 1 on 7H) were novel. Markers in common between the DArT and DArTseq datasets enabled integration of mapping results for LR response across the four breeding populations and all QTL detected were visualised on a single map for validation. The adult plant resistance (APR) locus Rph20 was the only region detected in all field environments. Markers and their associated sequences identified in this study will be useful for building QTL combinations involving Rph20, thereby providing stable LR resistance in improved barley cultivars. We will also highlight the advantages of AM using breeding germplasm over traditional bi-parental mapping approaches that underutilise genetic diversity and divert valuable resources into populations of low breeding value.

Stem rust is an important disease of wheat and barley. Barley is genetically vulnerable to stem rust with few identified resistance genes and sources. Stem rust resistance breeding is largely based on the gene Rpg1, first incorporated into North American barley cultivars in the 1940s. To identify potentially new resistance sources, the USDA-ARS National Small Grains Barley iCore Collection (1,860 accessions) was evaluated for reaction to stem rust at the seedling and adult stages. The adult stage evaluations were conducted at Njoro, Kenya (race TTKSK/TTKST), and St. Paul, Minnesota (race QCCJB), for two seasons, and the seedling tests (race TTKSK) in the BSL-3 greenhouse at St. Paul, Minnesota. At St. Paul, between 7 and 10% (132-203) of the accessions exhibited resistance, whereas in Kenya, 11-14% (218-261) were resistant. Correlation between years was higher in Kenya (0.60) than it was at St. Paul (0.48). Approximately 15% (277) of the collection gave moderately low to low reactions to TTKSK at the seedling stage. From these initial tests, 290 accessions were chosen based on diversity of reaction, origin of plant material, or stability across environments. These accessions were then further evaluated with a suite of races at the seedling stage to postulate resistance genes. Of these selections, 244 gave reactions suggesting they carry adult plant resistance. The remaining 46 accessions gave low to very low reactions to one or more races. Based on country of origin and resistance spectrum 15 accessions were predicted to have the rpg4/Rpg5 complex, including a subset from Switzerland. The remaining 31 have a reaction spectrum, country of origin or pedigree that does not suggest the presence of the rpg4/Rpg5 complex. Molecular tests will be used to confirm the presence of this complex in these materials.